by Ashifa

Hi,
I have a few questions to throw out and I would appreciate answers for any or all of these questions.
Firstly, can anyone explain, or recommend a site that can explain where on the coagulation cascade PTT and PT/INR kick in and how drugs like Heparin and Warfarin fit in to changing these parameters.
Secondly, what does INR stand for and if INR/PT tell us the same thing, why are they given two different names?
Lastly, what lab tests reflect the fibrinogen level?

Thank you

A good place to start is with drug companies. The makers of Coumadin, Heparin, tPA, and other drugs affecting clotting have all the info you can imagine. Sorry I don't have that info handy for you. You could do a web search using the name of the drug and get the information your looking for.

i hope this helps 1st there is a specific test you run for fibrinogen levels the normals are 200-400mg/dl. 2nd of all,heparin prevents the conversion of prothrombin to thrombin and neutralizes the clooting action of thrombin. The PTT reflects your heparin levels relatively speaking and is reversed by protamine sulfate. Coumadin inhibits the synthesis of prothrombin, measured by the PT and is reversed by aquamephyton(vit K). I hope that helps

i almost forgot, the INR stands for International Normalized Ratio.

The INR (international normalized ration) is a method of standardizing the test for coumading anticoagulation. Before the INR, different labs using different reagents had different controls in other words at my hospital a PT of 15 might be WNL and at hospital B 15 might be elevated. That makes it all rather confusing. The INR is the same everywhere. For anticoagulation in afib for example you want a target INR of 2 to 2.5 where for a patient with a mechanical valve the INR should be 2.5 to 3.

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Hello,
I have some information that may be helpful regarding the questions you asked.
An article, Monitoring Warfarin Therapy, from Nursing 99, pp 41-44, is a very good resourse to help you understand the PT and INR. I will be referring to this article throughout my explaination. I greatly encourage you to read this article.
Warfarin is the most commonly used anticoagulant that is used to help prevent clots or the extension of clots for many conditions. It inactivates vitamin K, which is part of the clotting cascade. Without vitamin K, the liver can't activate proteins necessary to form and maintain a clot (Oertel, pg 42). Prothrombin time results are not as accurate as that of the INR, which stand for International Normalized Ratio, because the thromboplastin reagents that are added to the blood vary from lab to lab, resulting in inaccurate readings. To understand the INR it is best to read the section of the article, INR: Leveling the playing field, I will try to summarize it for you. The INR was designed to standardize values and provide a more accurate assessment of a patient's anticoagultion intensity level regardless of the reagent used. As stated in the article, The INR is a mathematical correction to the prothrombin time ratio (PTR), (a value that's calculated using the patient's PT divided by the mean normal PT). So, as you can see, the PT and INR are not and do not tell us the same thing. The PT is a test, and the INR is not. The INR range is either that of 2.0-3.0 or 2.5-3.5, depending upon the condition in which warfarin is being used.
Heparin forms complex with a plasma co-factor, antithrombin III, which is a protease inhibitor that controls the activity of the following protease clotting factors: XIIa, XIa, IXa, Xa, IIa. Heparin antithrombin III complex with the clotting factors, thus in the presence with heparin, antithrombin III function is optimized. For heparin, the laboratory control of dose is done by activated PTT. PTT is activated partial thromboplastin time.
And lastly, the lab test that reflects the fibrinogen level is simply called the fibrinogen test, which indicates the level. The normal range is 200-400 mg/dcl.
I hope this information will help you.


[This message has been edited by Tracee (edited November 23, 1999).]

[This message has been edited by Tracee (edited November 23, 1999).]